Millimeter wave wafer level chip scale packaging (wlcsp) device and related method

ABSTRACT

Various embodiments include wafer level chip scale package (WLCSP) structures and methods of tuning such structures. In some embodiments, the WLCSP structure includes: a printed circuit board (PCB) trace connection including at least one PCB ground connection connected with a PCB ground plane; a set of ground solder balls each contacting the printed circuit board trace connection; a set of chip pads contacting each of the ground solder balls in the set of ground solder balls; a chip ground plane connecting the set of chip pads; and a signal interconnect interposed between two of the set of ground solder balls, the signal interconnect including: a signal trace connection electrically isolated from the PCB ground plane; a signal ball contacting the signal PCB trace connection; a chip pad contacting the signal ball, and a signal trace connection on a chip contacting the chip pad.

FIELD

The subject matter disclosed herein relates to interconnect devices forintegrated circuits. More particularly, the subject matter relates tomillimeter wave wafer level chip scale packaging (WLCSP).

BACKGROUND

As silicon technologies have advanced, the bandwidth at which circuitsutilizing those technologies can perform has also advanced. Packagingthese circuits (e.g., those capable of bandwidths up to approximately100 Giga-Hertz (GHz)) can be particularly challenging as silicontechnologies have advanced. Some conventional approaches have involvedusing wafer level chip scale packaging (WLCSP) for some millimeter-wavecircuit products. WLCSP involves mounting a chip directly on a printedcircuit board (PCB), eliminating the need for a package carrier(employed in older approaches).

However, conventional WLCSP has shortcomings, including for example: a)standard conventional WLCSP uses relatively large ball diameters(approximately 250 micrometers (um) for 400 um pitch-minimum ball pitchon PCB for current cost effectiveness) and height (approximately 200 umfor 250 um ball diameter). This conventional WLCSP has been shown toincur a −10 dB return loss bandwidth of approximately 70 GHz; and b)specialized conventional WLCSP designs use relatively small balldiameters, e.g., approximately 30 um to approximately 100 um, which mayextend the bandwidth of the packaging to approximately 100 GHz. However,the specialized designs have higher manufacturing costs (relative to thestandard designs), can cause wafer test issues due to the small ballsize, and can also have performance inconsistency between designsutilizing and not utilizing PCB pads, which may result in wafer testyield issues.

BRIEF DESCRIPTION

Various embodiments described include wafer level chip scale package(WLCSP) structures and methods of tuning such structures. In someembodiments, the WLCSP structure includes: a printed circuit board (PCB)trace connection including at least one PCB ground connection (i.e. aPCB via) connected with a PCB ground plane; a set of ground solder ballseach contacting the printed circuit board trace connection; a set ofchip pads contacting each of the ground solder balls in the set ofground solder balls; a chip ground plane connecting the set of chip pads(e.g., through a set of chip via arrays); and a signal interconnectinterposed between two of the set of ground solder balls, the signalinterconnect including: a signal trace connection electrically isolatedfrom the PCB ground plane; a signal ball contacting the signal traceconnection; a chip pad contacting the signal ball; and a signal trace ona chip contacting the chip pad.

A first aspect includes a wafer level chip scale package (WLCSP)structure having: a printed circuit board (PCB) trace connectionincluding at least one PCB ground connection connected with a PCB groundplane; a set of ground solder balls each contacting the printed circuitboard trace connection; a set of chip pads contacting each of the groundsolder balls in the set of ground solder balls; a chip ground planeconnecting the set of chip pads; and a signal interconnect interposedbetween two of the set of ground solder balls, the signal interconnectincluding: a signal trace connection electrically isolated from the PCBground plane; a signal ball contacting the signal trace connection; achip pad contacting the signal ball; and a signal trace on a chipcontacting the chip pad.

A second aspect includes a wafer level chip scale package (WLCSP)structure including: a printed circuit board (PCB) trace connectionincluding at least one PCB ground connection connected with a PCB groundplane; a set of ground pillars each contacting the printed circuit boardtrace connection; a set of chip pads contacting each of the groundpillars in the set of ground pillars; a chip ground plane connecting theset of chip pads; and a signal interconnect interposed between two ofthe set of ground pillars, the signal interconnect including: a signaltrace connection electrically isolated from the PCB ground plane; asignal pillar contacting the signal trace connection; a chip padcontacting the signal pillar; and a signal trace on a chip contactingthe chip pad.

A third aspect includes a method of tuning a wafer level chip scalepackage (WLCSP) structure, the method including: providing the WLCSPstructure including: a printed circuit board (PCB) trace connectionincluding at least one PCB ground connection connected with a PCB groundplane, wherein the PCB ground plane includes an opening; a set ofcontact devices each contacting the printed circuit board traceconnection; a set of chip pads contacting each of the contact devices inthe set of contact devices; a chip ground plane connecting the set ofchip pads, the chip ground plane including an opening; and a signalinterconnect interposed between two of the set of contact devices, thesignal interconnect including: a signal trace connection electricallyisolated from the PCB ground plane; a signal contact device contactingthe signal trace connection; a chip pad contacting the signal contactdevice; and a signal trace on a chip contacting the chip pad;determining a performance parameter of the WLCSP structure; and tuning asize of at least one of the opening in the PCB ground plane or theopening in the chip ground plane based upon the determined performanceparameter.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various embodiments of the invention, in which:

FIG. 1 shows a three-dimensional depiction of a wafer level chip scalepackaging (WLCSP) structure including solder balls according to variousembodiments.

FIG. 2 shows a two-dimensional graphical depiction of simulatedperformance parameters for a conventional WLCSP structure includingsolder balls.

FIG. 3 shows a two-dimensional graphical depiction of simulatedperformance parameters for a WLCSP structure including solder balls anda printed circuit board (PCB) according to various embodiments.

FIG. 4 shows a two-dimensional graphical depiction of simulatedperformance parameters for a WLCSP structure including solder balls andexcluding a PCB according to various embodiments.

FIG. 5 shows a three-dimensional depiction of a wafer level chip scalepackaging (WLCSP) structure including copper pillars according tovarious alternative embodiments.

FIG. 6 shows a two-dimensional graphical depiction of simulatedperformance parameters for a conventional WLCSP structure includingpillars and a printed circuit board (PCB).

FIG. 7 shows a two-dimensional graphical depiction of simulatedperformance parameters for a conventional WLCSP structure includingpillars and excluding a PCB.

FIG. 8 shows a two-dimensional graphical depiction of simulatedperformance parameters for a WLCSP structure including pillars and a PCBaccording to various embodiments.

FIG. 9 shows a two-dimensional graphical depiction of simulatedperformance parameters for a WLCSP structure including solder balls andexcluding a PCB according to various embodiments.

FIG. 10 shows a flow diagram illustrating processes according to variousembodiments.

It is noted that the drawings of the invention are not necessarily toscale. The drawings are intended to depict only typical aspects of theinvention, and therefore should not be considered as limiting the scopeof the invention. In the drawings, like numbering represents likeelements between the drawings.

DETAILED DESCRIPTION

As noted, the subject matter disclosed herein relates to interconnectdevices for integrated circuits. More particularly, the subject matterrelates to millimeter wave wafer level chip scale packaging (WLCSP).

As described herein, conventional WLCSP has shortcomings, including forexample: a) standard conventional WLCSP uses relatively large balldiameters (currently approximately 250 micrometers (um) for 400 umpitch-minimum ball pitch on PCB for cost effectiveness) and height(approximately 200 um for 250 um ball diameter). However, thisconventional WLCSP has been shown to incur a −10 dB return lossbandwidth of approximately 70 GHz; and b) specialized conventional WLCSPdesigns use relatively small ball diameters, e.g., approximately 30 umto approximately 100 um, which may extend the bandwidth of the packagingto approximately 100 GHz. However, the specialized designs have highermanufacturing costs (relative to the standard designs), can cause wafertest issues due to the small ball size, and can also exhibit performanceinconsistency between designs utilizing and not utilizing PCB pads,which may result in wafer test yield issues.

Various embodiments of the invention include WLCSP designs and relatedmethods of use that provide relatively high bandwidth (e.g.,approximately 100 GHz) with or without PCB pads, allowing forperformance consistency which makes wafer level testing more accurate.

Various embodiments of the invention include a WLCSP for millimeter waveapplications which can realize one or more of the following benefits:

A) The design considers a full path from the chip pad to the PCB padthrough the solder ball;

B) The design utilizes a targeted (e.g., optimized) solder ball size(e.g., approximately 120 to approximately 180 um diameter andapproximately 100 to approximately 150 um height), with correspondingchip pad and passivation opening sizes;

C) The design utilizes a solder ball pitch that is available for directPCB mount productions (e.g., approximately 400 um pitch);

D) The design utilizes PCB pad and solder mask opening sizes compatiblewith conventional PCB manufacturing with an in-pad standard via, whichmay utilize either solder mask defined (SMD) pads or non solder maskdefined pads (NSMD);

E) The design utilizes the edge solder ball path for signal with fivesurrounding ball paths as the ground or return path, giving awell-defined, enclosed signal path;

F) The design conforms to both chip and PCB design rules for coping withavailable chip and PCB processes; and/or

G) The design may utilize underfill for improved reliability of chip toPCB interconnections.

Additional benefits of the various aspects of the invention include: a)extending the WLCSP bandwidth beyond approximately 100 GHz, as comparedwith the standard design bandwidth of approximately 70 GHz; b)approximately the same low cost when compared with the standard WLCSPdesign; and/or c) consistent performance with or without the PCB pads,so that wafer tests can indicate accurate chip performance.

Various particular embodiments of the invention include a wafer levelchip scale package (WLCSP) structure having: a printed circuit board(PCB) trace connection including at least one PCB ground connection(i.e. a PCB via) connected with a PCB ground plane; a set of groundsolder balls each contacting the printed circuit board trace connection;a set of chip pads contacting each of the ground solder balls in the setof ground solder balls; a chip ground plane connecting the set of chippads (through a set of chip via arrays); and a signal interconnectinterposed between two of the set of ground solder balls, the signalinterconnect including: a signal trace connection electrically isolatedfrom the PCB ground plane; a signal ball contacting the signal traceconnection; a chip pad contacting the signal ball; and a signal trace ona chip contacting the chip pad.

Various additional particular embodiments of the invention include awafer level chip scale package (WLCSP) structure including: a printedcircuit board (PCB) trace connection including at least one PCB groundconnection (i.e. a PCB via) connected with a PCB ground plane; a set ofground pillars each contacting the printed circuit board traceconnection; a set of chip pads contacting each of the ground pillars inthe set of ground pillars; a chip ground plane connecting the set ofchip pads (through a set of chip via arrays); and a signal interconnectinterposed between two of the set of ground pillars, the signalinterconnect including: a signal trace connection electrically isolatedfrom the PCB ground plane; a signal pillar contacting the signal traceconnection; a chip pad contacting the signal pillar; and a signal traceon a chip contacting the chip pad.

Further particular embodiments of the invention include a method oftuning a wafer level chip scale package (WLCSP) structure, the methodincluding: providing the WLCSP structure including: a printed circuitboard (PCB) trace connection including at least one PCB groundconnection (i.e. a PCB via) connected with a PCB ground plane, whereinthe PCB ground plane includes an opening; a set of contact devices eachcontacting the printed circuit board trace connection; a set of chippads contacting each of the contact devices in the set of contactdevices; a chip ground plane connecting the set of chip pads (through aset of chip via arrays), the chip ground plane including an opening; anda signal interconnect interposed between two of the set of contactdevices, the signal interconnect including: a signal trace connectionelectrically isolated from the PCB ground plane; a signal contact devicecontacting the signal trace connection; a chip pad contacting the signalcontact device; and a signal trace on a chip contacting the chip pad;determining a performance parameter of the WLCSP structure; and tuning asize of at least one of the opening in the PCB ground plane or theopening in the chip ground plane based upon the determined performanceparameter.

The term “trace connection” (or simply “trace”) is used herein to referto a single piece of metal shape on a metal layer, which electrically(and physically) connects components. It is understood that as usedherein, the term “contact device,” “contact devices,” “ground contactdevices” and/or “signal contact devices” can refer to one or both of asolder ball structure or a pillar structure. That is, the “contactdevice(s)” claimed herein can include solder ball structures and/orpillar structures, of which, some are ground or signal contact devices.

Turning to FIG. 1, a three-dimensional perspective view of a WLCSPstructure 2 (using solder balls) is shown according to variousembodiments. As shown, the WLCSP structure 2 can include a printedcircuit board (PCB) trace connection 4, (e.g., on the top metal/wiringlayer of the PCB), including at least one ground connection 6 (i.e. aPCB via) connected with a PCB ground plane 8 (on a differentmetal/wiring layer than the trace connection 4, e.g. the secondmetal/wiring layer of the PCB). That is, the PCB trace connection 4 iselectrically grounded in at least one location (ground connection 6),and in this example, two such locations (i.e. two PCB vias) are shown.Contacting the PCB trace connection 4 is a set of ground solder balls10, where each of the ground solder balls 10 is electrically connectedto the PCB ground plane 8 via the PCB trace connection 4.

Overlying and contacting each the set of ground solder balls 10 is a setof chip pads 12 (e.g., integrated circuit chip pads normally on the lastmetal/wiring layer of the chip), where each chip pad 12 contacts adistinct solder ball 10 in the set of solder balls 10. Each chip pad 12is therefore connected to the PCB ground plane 8 via a solder ball 10and the PCB trace connection 4.

Each chip pad 12 is connected with a chip ground plane 14, which is on adifferent chip metal/wiring layer than the chip pad (e.g. the secondmetal/wiring layer of the chip), through a chip via array 12′ (theannular square ring). The chip ground plane 14 can be connected to thechip ground via any conventional connection (e.g., any conventionalground connection, not shown). As shown, the PCB trace connection 4,ground solder balls 10, chip pads 12, chip via array 12′ and chip groundplane 14 form a “C-shaped” or semi annular shape having an opening 16 ina region interposed between two of the ground solder balls 10.

According to various embodiments, a signal interconnect 20 is interposedbetween two of the ground solder balls 10 (in the opening 16). Thesignal interconnect 20, the chip ground opening 16 and the PCB groundopening 29, as described herein, are configured to tune the WLCSPstructure 2 in order to control the performance (e.g., return loss) ofthe WLCSP structure 2. The signal interconnect 20 can include: a signaltrace connection 22 on the top metal/wiring layer of the PCB, which iselectrically isolated from the PCB ground plane 8, where the PCB groundplane 8 is on a different metal/wiring layer of the PCB than the signaltrace connection 22. The signal interconnect 20 can also include asignal ball 24 contacting the signal trace connection 22, and a chip pad26 contacting the signal ball 24. According to various embodiments, thesignal trace connection 22 forms a microstrip line with the PCB groundplane 8 for carrying a signal. In various embodiments, the WLCSPstructure 2 can include a signal trace 28, which may be on the same chipmetal/wiring layer as the chip pads 12 (i.e. the last metal/wiringlayer) and is electrically connected with the chip pad 26 contacting thesignal ball 24. The signal trace 28 is electrically isolated from thechip side ground plane 14 (on a different chip metal/wiring layer, e.g.the second metal/wiring layer of the chip), forming an on-chipmicrostrip line with the chip side ground plane 14.

In some cases, the set of ground solder balls 10 and signal solder ball24 can have a substantially equal diameter. That is, each solder ball issubstantially the same size. As will be described herein, a diameter ofthe solder ball is directly related to a signal performance parameter inthe WLCSP structure 2. That is, the diameter of the solder balls cancontrol an amount of the signal loss in the WLCSP structure 2. In thissense, the signal loss of the WLCSP structure 2 is modifiable (tunable)by modifying a diameter of the solder balls.

In various embodiments, the WLCSP structure can utilize solder maskdefined or non solder mask defined pads for connection of the solderballs (10 and 24) to the PCB trace connection (4 and 22).

In various embodiments, the WLCSP structure can utilize underfill toimprove the reliability of the interconnection of solder balls (10 and24).

FIG. 2 shows a simulated performance parameter graph of a conventionalWLCSP device having a 260 um solder ball diameter with 400 um pitch.Line S21 represents the signal insertion loss from chip side to the PCBside, while S11 and S22 represent the return loss (i.e. signalreflection loss) of the chip side and PCB side, correspondingly. The −10dB return loss bandwidth of such conventional designs is slightly lessthan 70 GHz, with maximum in-band insertion loss of about 2 dB.

FIG. 3 shows the simulated performance of a WLCSP device according toembodiments of the invention, including a solder ball size of 160 umwith 400 um pitch. In these cases, the −10 dB return loss bandwidth ismore than 100 GHz with slightly less than 2 dB in-band insertion loss.FIG. 4 shows the simulated performance of the WLCSP device from FIG. 3,without a printed circuit board (PCB) present, i.e. the performance forthe WLCSP device with the solder balls only. In this case, the devicemaintains the −10 dB return loss bandwidth beyond 100 GHz with the samein-band maximum insertion loss of a little less than 2 dB. This impliesthat the wafer level chip tests can be accurately conducted on the WLCSPdevice.

FIG. 5 shows another WLCSP structure 102, which includes a printedcircuit board (PCB) trace connection 4 (e.g. on the top layer of PCB)including at least one ground connection 6 (i.e. a PCB via) connectedwith a PCB ground plane 8, which is on a different PCB metal/wiringlayer than the trace connection 4 (e.g. on the second metal/wiring layerof the PCB). It is understood that commonly numbered elements can depictsubstantially similar components between the Figures. That is, the PCBtrace connection 4 is electrically grounded in at least one location(ground connection 6), and in this example, two such locations are shown(i.e. two PCB vias). Contacting the PCB trace connection 4 is a set ofground pillars 110, where each of the ground pillars 110 is electricallyconnected to the PCB ground plane 8 via the PCB trace connection 4.

Overlying and contacting each the set of ground pillars 110 is a set ofchip pads 12 (e.g., integrated circuit chip pads, normally on the lastmetal/wiring layer of the chip), where each chip pad 12 contacts adistinct ground pillars 110 in the set of ground pillars 110. Each chippad 12 is therefore connected to PCB ground plane 8 via a ground pillar110 and the PCB trace connection 4.

In various embodiments, each ground pillar 110 can include a pillarsection 112 contacting a corresponding chip pad 12 in the set of chippads. Each ground pillar 110 can also include a solder joint 114contacting the pillar section 112 and the PCB trace connection 4.

Each chip pad 12 is connected with a chip ground plane 14, which is on adifferent chip metal/wiring layer than the chip pad (e.g. the secondmetal/wiring layer of the chip), through a chip via array 12′ (theannular square ring). The chip ground plane 14 can be connected to achip ground via any conventional connection (e.g., via conventionalground connection, not shown). As shown, the PCB trace connection 4,ground pillars 110, chip pads 12, chip via arrays 12′ and chip groundplane 14 form a “C-shaped” or semi annular shape having an opening 16 ina region interposed between two of the ground pillars 110.

According to various embodiments, a signal interconnect 120 isinterposed between two of the ground pillars 110 (in the opening 16).The signal interconnect 120, the chip ground opening 16 and a PCB groundopening 129, as described herein, are configured to tune the WLCSPstructure 102 in order to control the performance of the WLCSP structure102. The signal interconnect 120 can include: a signal trace connection22 on the top metal/wiring layer of the PCB (i.e. the top metal/wiringlayer of the PCB) which is electrically isolated from the PCB groundplane 8, where the PCB ground plane 8 is on a different metal/wiringlayer of the PCB (e.g. the second metal/wiring layer of the PCB) thanthe signal trace connection 22. The signal interconnect 120 can alsoinclude a signal pillar 124 contacting the signal trace connection 22,and a chip pad 26 contacting the signal pillar 124. In variousembodiments, the signal trace connection 22 forms a microstrip line withthe PCB ground plane 8 for carrying a signal. In various embodiments,the WLCSP structure 102 (and particularly, the signal interconnect 120),can include a signal trace 28, which may be on the same chipmetal/wiring layer as the chip pads 12 (i.e. the last metal/wiring layerof the chip) and is electrically connected with the chip pad 26contacting the signal pillar 124. The signal trace 28 is electricallyisolated from the chip side ground plane 14 (on a different chipmetal/wiring layer, e.g. the second metal/wiring layer of the chip). Thesignal trace 28 forms an on-chip microstrip line with the chip groundplane 14.

In various embodiments, the signal pillar 124 can include a pillarsection 126 contacting the chip pad 26, and a solder joint 128contacting the pillar section 126 and the signal trace connection 22.The dimensions (e.g., thickness and/or height) of the signal pillar 124can be modifiable by modifying the pillar section 126 and/or the solderjoint 128.

In some cases, the set of ground pillars 110 and the signal pillar 124can have a substantially equal dimension, as measured along the x or yaxis (diameter) and z axis (height). That is, each pillar issubstantially the same size. As will be described herein, a size of thepillars is directly related to a signal performance (including, e.g.,signal return and/or insertion loss) in the WLCSP structure 102. Thatis, the size of the pillars can control an amount of the signalinsertion loss and/or signal return loss in the WLCSP structure 102. Inthis sense, the signal return and/or insertion loss of the WLCSPstructure 102 is modifiable (tunable) by modifying a size (dimension) ofthe pillars.

In various embodiments, the WLCSP structure can utilize non solder maskdefined pads for connection of the solder joint (114 and 128) to the PCBtrace connection (4 and 22).

In various embodiments, the WLCSP structure can utilize underfill toimprove the reliability of the copper pillar (112 and 126) and solderjoint (114 and 128) interconnection.

FIG. 6 shows a simulated performance graph of a conventional WLCSPdesign using an 80 um diameter pillar with 400 um pitch. In thisconventional case, the −10 dB return loss bandwidth is higher than 100GHz with in-band maximum insertion loss less than 1.5 dB. As shown inFIG. 7, a problem (return loss) arises when the PCB does not present,i.e. under wafer test conditions, where the −10 dB return loss bandwidthdrops to about 60 GHz, as shown in FIG. 7. This problem can cause yieldloss during wafer tests. FIG. 8 and FIG. 9 show simulated performancegraphs of a WLCSP structure according to embodiments of currentinvention, including 120 um diameter pillars with 400 um pitch with PCB(FIG. 8) and without PCB (FIG. 9). Both graphs show the −10 dB returnloss bandwidth better than 100 GHz with similar maximum in-bandinsertion loss of about 1.5 dB.

Various embodiments of the invention include methods of tuning a waferlevel chip scale package (WLCSP) structure (e.g., the WLCSP structure 2and/or WLCSP structure 102 shown and described herein).

A general process can include:

Process PA: providing a WLCSP structure (e.g., WLCSP structure 2 and/orWLCSP structure 102 shown and described herein);

Process PB: determining a performance parameter of the WLCSP structure;

Process PC: tuning a size of at least one of the opening in the PCBground plane or the opening in the chip ground plane based upon thedetermined performance parameter. In some cases, the tuning includes atleast one of: determining a distance between at least two ground contactdevices in the set of ground contact devices; determining a dimension ofat least one ground contact device in the set of ground contact devices;determining a size of at least one chip pad in the set of chip pads;determining a size of at least one of the signal trace connectionelectrically isolated from the PCB ground plane or the signal traceconnection on the chip contacting the chip pad; or determining a size ofat least one of the opening in the PCB ground plane or the opening inthe chip ground plane;

Process PD (optionally): modifying a size of the signal contact deviceand the ground contact devices based upon the determined performanceparameter. In some cases, the set of ground contact devices includes atleast one of a set of solder balls or a set of pillars. In some cases,the signal contact device includes at least one of a solder ball or apillar.

FIG. 10 shows an illustrative flow diagram including particularprocesses according to various embodiments. As shown, the method caninclude the following processes:

Process P1: providing a WLCSP structure (e.g., WLCSP structure 2 and/orWLCSP structure 102 shown and described herein);

Process P2: determining a solder ball or pillar or contact pitch basedon PCB process restraint, PCB pad size required by in-pad via and PCByield/cost considerations, e.g. a pitch of 400 um to 1000 um for anormal PCB process;

Process P3: determining pad sizes for both chip and PCB based on chipand PCB process restraints;

Process P4: determining the signal trace connection width for both chipand PCB based on microstrip characteristic impedance needed, e.g. 50ohms;

Process P5: determining solder ball, pillar or contact size based on thecharacteristic impedance needed, e.g. choose the lateral size (diameter)to have the signal solder ball, pillar or contact to present a 50 Ohmcharacteristic impedance with the surrounding 5 ground solder balls,pillars or contacts vertically. In some alternative embodiments, the 5ground solder balls, pillars or contacts may be reduced to 4 by removethe middle one and associated chip pad/chip via array, which is at thecenter of the semi annular shape;

Process P6: checking the overall performance from chip signal traceconnection to PCB signal trace connection, such as insertion loss andreturn loss;

Decision D7: determining whether the performance meets the request, e.g.some design requests better than 1 dB insertion loss and 10 dB returnloss bandwidth, for very high frequency, the request can be only 10 dBreturn loss bandwidth with no significant dip/peak in the return loss;

Process P8 (No to Decision D7): tuning the ground opening sizes toimprove the performance. Then repeating process P6;

Process P9 (Yes to Decision D7): checking the performance from chipsignal trace connection to the bottom of the solder ball, pillar orcontact. This simulates the wafer test situation in which the PCB is notpresent;

Decision D10: determine whether “wafer only” performs similar to thecase with PCB, such as similar −10 dB return loss bandwidth and in-bandinsertion loss;

Process P11 (No to decision D10): tuning the solder ball, pillar orcontact size and/or ground opening sizes, and returning to process P6.

If Yes to Decision D10, End.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. It is further understood that theterms “front” and “back” are not intended to be limiting and areintended to be interchangeable where appropriate.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A wafer level chip scale package (WLCSP) structure comprising: aprinted circuit board (PCB) trace connection including at least one PCBground connection connected with a PCB ground plane; a set of groundsolder balls each contacting the printed circuit board trace connection;a set of chip pads contacting each of the ground solder balls in the setof ground solder balls; a chip ground plane connecting the set of chippads; and a signal interconnect interposed between two of the set ofground solder balls, the signal interconnect including: a signal traceconnection electrically isolated from the PCB ground plane, wherein thesignal trace connection electrically isolated from the PCB ground planeincludes a conductive strip which forms a microstrip line with the PCBground plane for carrying a signal; a signal ball contacting the signaltrace connection; a chip pad contacting the signal ball; and a signaltrace connection on a chip contacting the chip pad.
 2. (canceled)
 3. TheWLCSP structure of claim 1, wherein the signal trace connection on thechip includes a conductive strip on the chip that forms an on-chipmicrostrip line with the chip ground plane.
 4. The WLCSP structure ofclaim 1, wherein the chip ground plane includes an opening above thesignal chip pad, and the PCB ground plane includes an opening underneaththe signal solder ball for performance tuning.
 5. The WLCSP structure ofclaim 1, wherein a diameter of the signal ball controls an amount ofsignal loss in the WLCSP structure.
 6. The WLCSP structure of claim 1,wherein the set of ground solder balls and signal solder ball each havea substantially equal diameter. 7-19. (canceled)
 20. The WLCSP structureof claim 5, wherein the amount of the signal loss of the WLCSP structureis tunable by modifying the diameter of the signal ball.
 21. The WLCSPstructure of claim 4, wherein the opening above the signal chip padleaves the signal chip pad exposed above the chip ground plane.
 22. TheWLCSP structure of claim 4, wherein the chip ground plane forms a semiannular shape having the opening above the signal chip pad, the openingabove the signal chip pad located in a region interposed between the twoof the set of ground solder balls.
 23. The WLCSP structure of claim 1,wherein the signal trace connection on the chip contacting the chip padis a single piece of metal.
 24. A wafer level chip scale package (WLCSP)structure comprising: a printed circuit board (PCB) trace connectionincluding at least one PCB ground connection connected with a PCB groundplane; a set of ground solder balls each contacting the printed circuitboard trace connection; a set of chip pads contacting each of the groundsolder balls in the set of ground solder balls; a chip ground planeconnecting the set of chip pads; and a signal interconnect interposedbetween two of the set of ground solder balls, the signal interconnectincluding: a signal trace connection electrically isolated from the PCBground plane, wherein the signal trace connection electrically isolatedfrom the PCB ground plane includes a conductive strip which forms amicrostrip line with the PCB ground plane for carrying a signal; asignal ball contacting the signal trace connection; a chip padcontacting the signal ball; and a signal trace connection on a chipcontacting the chip pad, wherein a diameter of the signal ball controlsan amount of signal loss in the WLCSP structure, wherein the chip groundplane includes an opening above the signal chip pad, and the PCB groundplane includes an opening underneath the signal solder ball forperformance tuning, wherein the chip ground plane forms a semi annularshape having the opening above the signal chip pad, the opening abovethe signal chip pad located in a region interposed between the two ofthe set of ground solder balls.